This is a bit off-topic but I'll go for it. Motor efficiency would roughly be input power to output power ratio. For a box fan, it would be Watts input vs CFM output and there is not anything one can do, that I am aware of, to improve the efficiency. Unfortunately too, most manufacturers short of showing an Energy Star certification, give no meaningful information about efficiency. In AC motors, usually the Brushless DC motor would be the most efficient (with suitable drive) - as well as the most expensive. Then comes 3 phase motors, which we never see outside of industrial applications. Next would be a capacitor run (split phase) motor. Those are common in ceiling fans. Least efficient of all are also the most common - the induction and shaded pole motors.

I believe that there has to be a match between the motor power sense and the BEMF sensing since the relevant signal is Motor+ (-) phase bemf.I did a search for "atmega8 bldc controller" and got a few hits. This one has a description http://davidegironi.blogspot.it/2013/09/a-simple-b... Some controllers monitor with the analog inputs. Some with a comparator input. It's all code dependent. There is a certain amount of tuning involved where the the controller is tuned for a motor with a given bemf constant. If your original motor worked with the controller and the modifed motor does not, it is likely because the stronger magnets will result in a higher bemf constant. Hope this helps...

Depends how the ESC works. Probably the microcomputer on the esc works off of the pulse width from the RC receiver. All the RC units I've worked with use a 1.5 mS (+/- 500 uS). That's 1 mS for min speed and 2 mS for max speed (or forward /reverse speed). No biggie to make this pulse with an oscillator like a NE555 or equivalent. Rep rate on the pulses is not critical and is in the vicinity of 50 Hz. Some systems use a positive pulse while others use a negative pulse. Be prepared to add an inverter.

As this is a brushless DC motor, what is being used for commutation? ie, does the motor have rotor position sensor like Hall effect sensors - or does it commutate based on back-emf? If it is the latter, the uP or dedicated motor controller if there is one, senses the voltage on one of the phases and makes decisions based on that. With a BLDC, two of the phases are energized and one is off at any given time. The phase that is not energized has a back-emf related to speed and rotor position... Perhaps you have to identify the voltage dividers on these and make sure that the resulting voltage is within the range of the controller's ADC. (btw- I am an electrical engineer)

I assume that when attaching the magnets, that one must alternate N and S poles? Unless you have a fancy gaussmeter, take any magnet and mark one face of it. Use this to test all the other magnets and arbitrarily mark the face that attracts or repels. Actually an inexpensive polarity checker is a Hall Effect sensor. The one I use is unipolar sensing and sensitive to a S pole approaching (off at zero flux and on for flux greater than...). My reference magnet that activates the sensor (I have a LED on the output) has this face marked "S". When using this to test other magnets, the face that repels, is also S.ESCs usually aren't too difficult to reverse engineer unless the vendor has sanded off all the parts markings. Some of the smaller SMT passives don't have any marking anyway...

I assume that when attaching the magnets, that one must alternate N and S poles? Unless you have a fancy gaussmeter, take any magnet and mark one face of it. Use this to test all the other magnets and arbitrarily mark the face that attracts or repels. Actually an inexpensive polarity checker is a Hall Effect sensor. The one I use is unipolar sensing and sensitive to a S pole approaching (off at zero flux and on for flux greater than...). My reference magnet that activates the sensor (I have a LED on the output) has this face marked "S". When using this to test other magnets, the face that repels, is also S.ESCs usually aren't too difficult to reverse engineer unless the vendor has sanded off all the parts markings. Some of the smaller SMT passives don't have any marking anyway and must be unsoldered to test with an appropriate RCL meter.

One thing to look out for is that older drives, especially IDE types, will draw more current than the typical 500 mA that a USB connector will supply. These may require a Y cable to capture the data from one USB port and the current from two USB ports.As with any USB connected storage devices, ALWAYS use the "Safely remove devices" function before unplugging. This closes any open files. Also, unplugging while the computer is in sleep or standby, will risk corruption of your external drive as files may still be open.That said, I didn't want to get a drive bay for my laptop (fits a hard drive in place of the DVD rom), I velcro'ed the external drive to the laptop's lid.